Şakir Erkoç

Empirical many-body potential energy functions used in computer simulations of condensed matter properties

Empirical many-body potential energy functions (EMBPEFs) are extensively used in atomistic computer simulations, especially in molecular dynamics and Monte-Carlo methods. There are several EMBPEFs used in the literature for different purposes, some of these functions are suitable for bulk and surface properties, and some of them are suitable for cluster properties. In this article the EMBPEFs used in the computer simulation applications for condensed matter properties will be reviewed.

AM1 treatment of endohedrally hydrogen doped fullerene, nH2@C60

Abstract Endohedrally hydrogen doped C60 systems, nH2@C60 (n: 9,12,15,19,21,24) have been theoretically investigated at the level of AM1 (RHF) type quantum chemical treatment. It has been found that n:24 is the maximum number of hydrogen molecules which should result a stable composite system. The calculations indicate that all these structures are stable but highly endothermic. Also some geometrical and physicochemical properties of these structures are reported.

Structural and electronic properties of single-wall BN nanotubes

Abstract The structural and electronic properties of armchair and zigzag models of single-wall BN nanotubes have been investigated by performing semi-empirical molecular orbital self-consistent field calculations at the level of the Austin Model 1 (AM1) method within the RHF formulation. It has been found that these structures are stable and exothermic. The armchair model has a zero net dipole moment, whereas the zigzag model has a nonzero net dipole moment. The interfrontier molecular energy gap of these systems are close to each other, thus the gap is independent of the chirality of the tube.

Theoretical investigation of quercetin and its radical isomers

The structural and electronic properties of quercetin and its five radical isomers have been investigated theoretically by performing semi-empirical molecular orbital theory calculations. The geometry of the systems have been optimized and the electronic properties of the systems considered have been calculated by semi-empirical self-consistend-field molecular orbital theory at the level AM1 within UHF formalism in their ground state. Conclusions have been drawn by comparing with experimental results.

Genetic Algorithms Applied to Li+ Ions Contained in Carbon Nanotubes: An Investigation Using Particle Swarm Optimization and Differential Evolution Along with Molecular Dynamics

Empirical potentials based upon two and three body interactions were applied to the Li+–C system, assuming the Li+ ions to be distributed inside high-symmetry, single walled carbon nanotubes of different chirality. Structural optimizations for various assemblages were conducted using evolutionary and genetic algorithms, where differential evolution and particle swarm optimization techniques worked satisfactorily. The results were compared with the outcome of some rigorous molecular dynamics simulations. The potential for using the carbon nanotubes in the negative electrode of lithium ion batteries was also critically examined.

Structural and electronic properties of endofullerenes X@C60.

Abstract Structural and electronic properties of certain endohedrally doped C60 has been investigated by performing semi-empirical molecular orbital calculation at PM3 level within RHF formalism. Hydrogenated B, C, N, Al, Si, and P atoms have been put into C60 as dopant. Hydrogenated aluminum dopant decreases the binding energy of fullerene, on the contrary it increases the heat of formation of the system. Furthermore hydrogenated aluminum and phosphorus dopants reduce the frontier molecular orbital energy gap of the system. Negative charge accumulation takes place on dopants in all the cases without generating the dipole moment. The endofullerenes, (MHn)@C60, have been found to be stable but endothermic.

Multilayer relaxation calculations for low index planes of an fcc crystal

Using a semi-empirical potential comprising two- and three-body interactions the multilayer relaxation for the low index planes (100), (110), and (111) of an fcc structure has been investigated. It has been found that the three-body forces are extremely important in the multilayer relaxation of surfaces. The most significant relaxation takes place for the first interlayer spacing, d12, which exhibits an expansion or contraction depending on the intensity of three-body interactions. Calculations produced results with correct trends which are in good agreement with recent experimental findings.

Ammonia deposition in fullerene: (NH3)n@C60

Abstract Deposition of ammonia molecules in fullerene has been investigated theoretically by performing semi-empirical molecular orbital calculation at PM3 level within RHF formalism. C60 cluster has been doped endohedrally by ammonia molecules. Structural and electronic properties of the systems considered have been studied. It has been found that C60 cluster can store at most six ammonia molecules. The ammoniacal endofullerenes, (NH3)n@C60, have been found stable but endothermic.

Structural and electronic properties of PFOS and LiPFOS

The structural and electronic properties of perfluorinated surfactants perfluorooctane sulfonate (PFOS) and lithium perfluorooctane sulfonate (LiPFOS) have been investigated theoretically by performing semi-empirical molecular orbital theory at the level of AM1 calculations. The optimized structure and the electronic properties of the molecules are obtained.

Electronic structure of carbon nanotubes: AM1-RHF calculations

Abstract We have investigated the electronic structure of optimized open-ended single-wall carbon nanotubes with armchair and zigzag geometries. The calculations were performed using AM1-RHF semiempirical molecular orbital method. It has been found that the density of states of the zigzag model is more sensitive to the tube size than that of the armchair model.